DEF Temperature Sensor Circuit Malfunction (Generic)
The P4065 code means the vehicle's onboard diagnostic system has detected: DEF Temperature Sensor Circuit Malfunction (Generic). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $150 - $500 (parts and labor)
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Common Symptoms
- Check Engine Light on
- DEF heating system not controlled properly
- Possible DEF freezing in cold weather
- DEF system warning
- Reduced DEF injection accuracy
Probable Causes (Ranked by Likelihood)
- Failed DEF temperature sensor Very High
- Wiring fault in DEF tank module High
- Connector corrosion from DEF Moderate
- PCM input circuit error Low
Step-by-Step Diagnostic Procedure
-
Test DEF temperature sensor resistance at known temperature
-
Inspect tank module connector
-
Check wiring for continuity
-
Compare DEF temperature to ambient at cold start
Frequently Asked Questions
Why does DEF temperature matter?
DEF freezes at 12 degrees F. The system needs temperature data to control the tank heater.
Can I drive with P4065?
You can drive short distances. In warm weather this is less critical.
Is the temperature sensor replaceable separately?
On most vehicles, it is part of the integrated tank module.
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